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<p>Many codes suggest admixtures to control water cement ratio, reduction in shrinkage, voids, creep, etc besides increasing the workability, strength, durability, etc parameters for the best performance of CC structures. As per Bureau of Indian Standards (BIS) IS:456 code, the upper limit of OP cement in a cubic meter of concrete is fixed at450 kgs. If the engineer require to use more than that upper limit, he has to take precautions against shrinkage, alkali silica reaction & cracking. Also, IS:456 says that for higher grades of concrete, beyond M55, its recommendations are not applicable. </p>
super plasticizers and water reducing agents shall be used for high cement content. Also, the more cement you add the more critical heat of hydration. for bulk casting that can cause huge cracks. going for such high limit without earlier experience will require you to perform testing on strength, heat of hydration, shrinkage, creep and other properties. see ASTM standards.Search for UHPC, HPC. you might find answers for your questions
never add cement or water, it will have effect on the Water- cement ratio, end so directly an effect on the quality ) strength) and environmental Class. More cement gives you more cracks, so more rebar is needed. Sometimes in cold weather we change the mixture by adding more or different type of cement. But always together with the concrete plant, the concrete experts.
The structural design with the needed quality is leading. changing this needs to be communicated with the structural engineer as well.
Aim of mix design is to get the mix ratios of the cement, sand, gravel, water, additives to attain the required design. Increasing cement ratio is good for higer design values with coordination of other ingredients, but it is expensive. Also it has higher hydration heat which is not wanted mostly.
more and more cement leads to shrinkage and cracks. Also, there will be a quantity of cement that won't react as there will be no water available and this quantity will actually be not cement, but aggregates in powder form- harmful for concrete's strength. The ratio water/cement is not something to play with...So, adding cement without consideration may result to a useless concrete mixture...
there is always limit for cement content and these limits are specified in mix design guidelines and also in specifications.. Extra cement in concrete will cause more shrinkage and will make concrete vulnerable to various atmospheric attack resulting in failure of concrete.. Make it a practice that any changes on site in concrete mix shall be done in presence of competent person who is handling particular mix and its trial.. It may depend on your client requirement also, as many concrete professionals strictly prohibit any alteration after mixing of concrete
for which company you are working? company is still there?
